Demand for secondary batteries as an energy source has been significantly increased as technology development and demand with respect to mobile devices have increased, and, among these secondary batteries, lithium secondary batteries having high energy density and high voltage have been commercialized and widely used.
Charge and discharge of the lithium secondary battery is performed while a process of intercalating and deintercalating lithium ions from a lithium metal oxide positive electrode into and out of a carbon negative electrode is repeated.
In this case, since the lithium ions are highly reactive, the lithium ions react with the carbon electrode to form Li2CO3, LiO, or LiOH, and thus, a film may be formed on the surface of the negative electrode. The film is denoted as “solid electrolyte interface (SEI) film”. The SEI film formed at an initial stage of charging may prevent a reaction of the lithium ions with the carbon negative electrode or other materials during charge and discharge, and may act as an ion tunnel that only passes the lithium ions between an electrolyte solution and the negative electrode. The ion tunnel may prevent the collapse of a structure of the carbon negative electrode due to the co-intercalation of the carbon negative electrode and organic solvents of the non-aqueous electrolyte solution having a high molecular weight which solvates the lithium ions and moves therewith.
In a case in which the organic solvent used in the non-aqueous electrolyte solution of the lithium secondary battery is generally stored for a long period of time at high temperature, gas is generated while the organic solvent is oxidized by a transition metal oxide discharged from the positive electrode, and battery swelling and electrode assembly deformation occur due to the gas thus generated. Furthermore, the negative electrode is exposed while the SEI film is gradually collapsed during high-temperature storage in a fully charged state (e.g., storage at 60° C. after charged to 100% at 4.2 V), and, since gases, such as CO, CO2, CH4, and C2H6, are generated while the negative electrode thus exposed reacts with the electrolyte solution to continuously cause a side reaction, deformation, such as battery swelling, due to an increase in battery internal pressure may eventually occur. When the battery is deteriorated due to internal short circuit of the battery which is caused by the battery deformation, fire or explosion of the battery may occur.
In order to address these limitations, a method of adding an SEI forming material for preventing the collapse of the SEI film in the non-aqueous electrolyte solution has been proposed. However, another limitation has occurred in which overall performance of the secondary battery is reduced while there are other side effects due to the electrolyte solution additive.
Thus, there is a continuous need to develop a non-aqueous electrolyte solution with a new configuration which may improve high-temperature and overcharge stability of the lithium secondary battery while minimizing the side effects.